DVDFab and Letterboxing... Please Help!

Hello everybody, sorry for my bad English and for being a newbie in video.

First: I own a Full HD 16:9 - 1.78:1 Philips TV

I have a problem that I cannot solve with DVDFab and I hope to find some help here.

I've got the .avi movie "Edge of Tomorrow" (but this happens whith other digital movies and formats) which DVDFab displays with a resolution of 1920px800p (2.40:1).

What I have is just in the exact format (with exact dimensions) of the movie without any letterboxing and DVDFab Converter shows me the movie like that, without any letterboxing (instead, when I insert a DVD, I can see the letterbox).

Of course what happens if I try to watch the movie on my TV is that I see a vertically stretched version of the movie where the height of the viewable image changes from 800p to 1080p as there is no letterboxing.

Now, from my calculations, if I have a TV with a 1.78:1 ratio and I want to see a movie with a HIGHER ratio than my TV and normal proportions, the new height for the (reduced) image is h=1920/r when r (ratio) in this case is 2.40.

In fact in this case h=1920/2.40=800 and it coincides with the original, not letterboxed format of the original image.

To keep the original 2.40:1 ratio of the image on my TV I should have letterboxing with two (bottom and top) black bars b=(1080p-800p)/2=140p which don't appear nor on my TV nor in DVDFab under the "Edit">"Info" option.

If I change the original format in DVDFab from "original" (2.40:1) to 16:9 I get again a vertically stretched image with same results as the original and there is no way to add the black bars to the original movie.

Same happens with movies with r=2.35:1 (h=816, b=132) etc....

Is there anybody out there who can help me solve this problem?

If you know there is any other software (possibly free) with a very simple and nice GUI that I can use I would be more than happy!